CVD Parameters Research Articles

Atomistic insights into chemical vapor deposition process of preparing silicon carbide materials using ReaxFF-MD simulation

SiC is a kind of key advanced coating material used widely. The in-depth understanding of the CVD process of preparing SiC materials at the atomic scale is beneficial for studying the CVD mechanism and then optimizing the materials. Here, a CVD model of preparing SiC materials is established based on ReaxFF-MD considering the whole pyrolysis-adsorption-desorption-growth mechanism. The accuracy of the ReaxFF potential and its parameters is verified by DFT at first. Then an energy-based Monte Carlo (EMC)-MD-CVD model is proposed based on the bonding formation energy originating from DFT. It is used to simulate the CVD process of preparing SiC materials. The CVD of MTS is studied by deposition efficiency and deposited film components at different temperatures, and it can be found it in good agreement with experimental results. Finally, the crystallization of SiC film prepared by the CVD of MTS is studied by energy evolution and atomic structure evolution. The results are helpful to understand the CVD mechanism for preparing coatings and it can be used to optimize the CVD parameters of preparing SiC materials in the future.

ХИМИЧЕСКОЕ ОСАЖДЕНИЕ ИЗ ГАЗОВОЙ ФАЗЫ ПИРОУГЛЕРОДНЫХ ПОКРЫТИЙ НА ПОРОШКАХ В ПСЕВДООЖИЖЕННОМ СЛОЕ. II. ПОЛУЧЕНИЕ ПОКРЫТИЙ

Pyrocarbon coatings of nanometer and submicron thickness were applied to coarse powders by Low Pressure Chemical Vapor Deposition (LPCVD), using a technical mixture of propane-butane. The nfluence of the nature of the carrier powder and CVD parameters on the deposition process was studied: total pressure (5 and 17 kPa), temperature (800, 900, 1000 °C), deposition time (0.5–3 h). The specific weight of the coatings was measured, the coatings thickness and the conversion degree of the reactant in the reactor were calculated, other engineering calculations were carried out. Design and technological solutions and research results are compared with those known from the literature

Effect of CVD parameters on large area growth of highly crystalline MoS2 thin flakes

In this study, we presented a report on effect of growth parameters (seeding promoter, growth temperature, Ar gas flow rate) on the formation of MoS2 monolayer. The morphology and structure of as-grown MoS2 were investigated in detail by optical microscopy, atomic force microscopy, Raman and photoluminesence spectroscopy techniques. The results showed that a highly reproducible growth of dense MoS2 triangular flakes with the size of ~35 µm over large area (~1.5x1 cm2) can be obtained by using a optimized parameters. The MoS2 field effect transistors based on the as-grown MoS2 exhibited carrier mobility of 0.5–2 cm2V−1s−1 and On/Off ratio of ~104. Our results can provide a useful information to realize large area, high quality of MoS2 for real electronic applications.

Bandgap tuning of Monolayer MoS2(1-x)Se2x alloys by optimizing parameters

Among the two-dimensional (2D) materials, transition-metal dichalcogenide (TMD) monolayer alloys attract significant attention as they allow for bandgap engineering, which is highly beneficial for their applications in nanoelectronics, optoelectronics, and photonics. In this research, we present a facile and repeatable molybdenum sulphoselenide (MoS2(1-x)-Se2x) monolayer growth through systematic investigation of CVD growth parameters such as gas flow rates, substrate temperature and precursor concentration (S/Se ratio). We have obtained a full control of the x values within the range of 0–1 allowing for bandgap tailoring between 1.82 eV (MoS2) and 1.56 eV (MoSe2) where the size of the grown monolayer flakes has been measured as large as 150 μm on SiO2 (300 nm)/Si substrates. We find that S/Se ratio and the growth temperature are the most critical parameters to control the composition (x value) of the monolayer alloy TMDs. In our study, we find two growth regimes, where S rich alloys are grown by controlling S to Se ratio at 750 °C and Se rich alloys are synthesized at higher growth temperatures (900 °C) by utilizing Se rich vapor conditions. Growth of Se rich alloys at a higher growth temperature is attributed to the chalcogen exchange mechanism (CEM) referring to substitution of S atoms in as grown alloy host lattice site with Se atoms present in the Se rich vapor. CEM is proposed as the basic alloying mechanism for selenium rich monolayer alloys. Regarding the structural properties, FWHM of the photoluminescence (PL) spectral peaks of our flakes range between 19 and 37 nm together with uniform spatial PL emission intensities indicating high crystalline quality. Tuning the bandgap of high-quality and large area TMD monolayers by simply changing the basic CVD parameters is of great benefit for future 2D optoelectronic devices.

CNT sponges with outstanding absorption capacity and electrical properties: Impact of the CVD parameters on the product structure

Abstract This work presents a detailed study of the influence of the synthesis parameters on the nanopowder-catalyzed CNT sponge production. Through electrochemical and absorption analyses, the sponges indicated a low resistivity (4.8x10−3 Ω m), capacitive behavior, very good cyclability and an elevated capacity of absorption of non-polar fluids (∼16 g/g). The polar character of the structure was easily modified by acid treatment allowing its further application in polar solutions. The produced sponge could be a practical tool for the recovery of water sources contaminated by non-polar substances. Additionally, it is a promising electrode in electrochemical processes with both polar and non-polar electrolytes.

Optimization of the CVD parameters for ZnO nanorods growth: Its photoluminescence and field emission properties

Vertically aligned single crystalline ZnO nanorods arrays were grown on a silicon substrate in a CVD reactor using Au as a catalyst. The CVD parameters such as substrate temperature, catalyst layer thickness/morphology and reaction time play a crucial role in the synthesis of nanostructures by the vapor-liquid-solid process. By optimizing these various CVD parameters, highly controlled guided growth of ZnO nanorods was achieved. The structural and morphological properties of resultant ZnO nanorods were studied by means of X-ray diffraction, high-resolution transmission electron microscopy, selected area electron diffraction and field emission scanning electron microscopy. The photoluminescence spectroscopy was also done to investigate the defects in grown ZnO nanorods. The field emission results of nanorods array indicated that the properties of the field emission follow Fowler–Nordheim law. The nanorods (grown for 20 min) are vertically aligned on the substrate surface without entanglements and with good crystal quality as well which is very important for several applications.

Direct Synthesis of Electrowettable Carbon Nanowall–Diamond Hybrid Materials from Sacrificial Ceramic Templates Using HFCVD

Carbon‐on‐carbon materials carry the potential to be a major disruptive technology in fields like energy storage and electronics. In the present work, hot filament chemical vapor deposition (HFCVD) is used to synthesize carbon nanowall (CNW) tetrapods coupled to nanocrystalline diamond in a 3D hybrid network form. The CNW/diamond phase proportion as well as the structural morphology can be easily adjusted by the CVD parameters, allowing a single‐step synthesis of CNW micro‐ and nanopillars or CNW/diamond 3D hybrid materials, in the powder form or as interconnected free‐standing specimens. Additionally, the direct incorporation of SnO2 catalyst particles during the one‐step CVD process is demonstrated. µ‐Raman and electron microscopy are used to understand the evolution of the morphological characteristics associated to the growth mechanism. The electrowettability behavior of the novel CNW/diamond hybrid material is demonstrated by electrochemical polarization studies. Such multifunctional carbon‐based hybrid 3D nanomaterials can find promising applications in advanced technologies such as energy storage.

(Invited) Thermodynamic Modeling of W-C-O-H-S System for Controlled Growth of WS2 Atomic Layers by True CVD

Objective: Layered TMDs such as MX2 (M = Mo, W; X = S, Se) are candidate materials for future electronic and optoelectronic devices. For integration of TMD-based devices into existing microelectronics technology, a CVD technique that allows controlled deposition of uniform layers over large areas is required. Further, to achieve layered heterostructures and doping, it is essential to develop a “true” CVD method in which all the precursors are vaporised outside the reactor, and enter the reactor with specific flows controlled by MFC’s. CVD growth of TMDs (WS2 growth is demonstrated here) is dictated by variation in process parameters like total reactor pressure P, growth temperature T and gas flow rate. Variation of these parameters over a wide range may lead to contamination in the form of carbon, carbides, sulfur, other sulfides, oxides and metal in different combinations. Uncontrolled compositional disturbances are extremely undesirable for electronic devices as they result in inconsistent background. Thermodynamic equilibrium calculations become essential at this point to select optimum operating conditions for contamination-free growth. Having identified the optimum growth window, gas phase supersaturation needs to be controlled such that layer controlled pure WS2 can be synthesized. The results obtained from thermodynamic analysis may then be used to design CVD processes, assuming that equilibrium prevails, an assumption valid when the rate of deposition is low. Computations on equilibrium compositions of the solid and gaseous species formed under various CVD conditions lead to the construction of “CVD phase stability diagrams”, to identify appropriate process window for growth of contamination-free WS2. To the best of our knowledge, there is no previous report for such modelling on this system. The objective is to construct this CVD diagram and compare it with experimental observations for the W-C-O-H-S system for controlled growth of WS2 layers. New Results: Equilibrium thermodynamic modeling of CVD, using W(CO)6 and H2S as precursors in Ar, Ar/H2 and H2 ambient, was investigated by minimizing the total Gibbs free energy in the W-C-O-H-S system. The ranges of CVD parameters used for the present calculation were: T=100-1100°C, P=10-900 Torr, and flow rate ratio W(CO)6:H2S:(Ar and/or H2) =1:(2-50):(100-1000). The ability of these phase diagrams in predicting growth outcomes is corroborated by the Raman spectroscopy data, XRD and XPS from samples deposited over a range of process parameters. A comprehensive CVD phase stability diagram for formation of solid phases in Ar ambient is demonstrated in Fig 1(a). It predicts the stability window for pure WS2 and indicates co-deposition of WS3 and C at lower T. Quantitative carbon contamination of WS2 films for wide variation in T and P is depicted in a contour plot in Fig. 1(b). Increasing carbon contamination of WS2 at lower T and higher P is validated by Raman spectra depicted in Fig. 1(c). This makes Ar unsuitable as carrier gas for growth, as higher P is required to achieve the reduction in supersaturation that is critical to obtain uniform layers of desired thickness. Modeling predicts, however, that the deposition of carbon can be precluded by increasing the partial pressure of hydrogen, i.e., by using a mixture of Ar and H2 as the carrier gas, as shown in Fig 1(d). In Ar/H2 and in H2 ambient, the stability domain of carbon narrows as P is increased, meeting the criterion for reduction in supersaturation. Pure H2 as a carrier gas is shown to facilitate the largest contamination free process window. CVD phase stability diagram in H2 ambient, predicting the ranges of CVD conditions for growth of contamination-free WS2, is illustrated in Fig. 1(e). WC and W deposit in various combinations for process parameters beyond this range. Raman spectroscopic data [Fig. 1(f)] showing carbon-free WS2 for wide ranges of P and T validates the phase diagrams in H2 ambient. Given the multivariable nature of the problem, excellent agreement between theoretical and experimental results was observed. Conclusion: A generic approach suitable to all TMDs, involving a combination of thermodynamic modeling and kinetic control for desired growth, is explored for the system W-C-O-H-S. Thermodynamic equilibrium calculations serve as a first step to determine process parameter windows for the desired end product. The ability to predict the completely different outcomes on using Ar versus Ar + H2 mixture as the carrier gas highlights the importance of such thermodynamic modeling. Thus, theoretical analysis of the CVD process can be employed to synthesize desired films in a predictive manner. This reduces the effort and resources needed for process development, and aims to bring a systemic approach to hitherto ad-hoc process. Figure 1

Review—Critical Considerations of High Quality Graphene Synthesized by Plasma-Enhanced Chemical Vapor Deposition for Electronic and Energy Storage Devices

Graphene is a promising electrode material not only due to its intrinsic properties like good electrical conductivity, high mechanical strength and high chemical stability, but also because of its high theoretical surface area of 2630 m2 g−1. In this report, the effect of CVD parameters to the growth of high quality graphene on metal substrates by using plasma enhanced chemical vapor deposition (PECVD) was extensively studied. Interestingly, synthesizing high quality graphene by PECVD technique is not only depending on the CVD parameters, but also depending on the catalysts and its plasma sources. It was found that Ni and Cu are the most favored metal catalysts for PECVD graphene growth. With high solubility of carbon (> 0.1 at. %), Ni effectively promote the growth of multilayer graphene by PECVD. However, large-area synthesis has made relatively inexpensive Cu as one of the most attractive substrates for monolayer graphene growth. Further details on the potential use of different transition metal catalysts in synthesizing graphene and consequently the specific usage of graphene based devices are discussed in this report.

Theoretical and experimental influence of aerosol assisted CVD parameters on the microstructural properties of magnetite nanoparticles and their response on the removal efficiency of arsenic

The development and optimization of methodologies to generate magnetite nanoparticles is currently an innovation topic. For a desired application such as arsenic removal from waste water, the generation of these nanostructures with specific microstructural properties is determinant. Therefore, it is necessary to understand the phenomenon during the nanoparticles formation process. Thus, in this work it is reported the influence of synthesis parameters of AACVD technique on the formation of magnetite nanoparticles. Parameters were according to: (1) synthesis temperature, (2) tubular reactor diameter, (3) concentration of the precursor solution and type of solvent, (4) carrier gas flow and (5) solvent type in the collection process. The effect of these synthesis parameters on the morphology, size and microstructure are discussed in detail and related with the mechanism of formation of the particles. Theoretical simulations were performed on two of these parameters (1 and 4). The microstructure and surface morphology of the different nanostructures obtained were characterized by field emission scanning electron and transmission electron microscopy. Subsequently two materials, were selected for further microstructural analysis. Finally, to determine the removal efficiency in the two materials the arsenic adsorption was evaluated. A major contribution of this work was the calculation of the number of spherical particles formed from a single drop of precursor solution. This calculation matched with the value found experimentally.

Tracking of cardiovascular risk factors from childhood to young adulthood — the Pune Children's Study

Tracking of cardiovascular risk factors from childhood to young adulthood — the Pune Children's Study

Effect of Coenzyme Q10 and Ardisia japonica Blume (AJB) on plasma and liver lipids, platelet aggregation and RBC Na efflux channels in simvastatin treated hypercholesterolemic guinea pigs

Forty guinea pigs were divided into four groups and fed 0.5% cholesterol based control diet, plus 0.05% simvastatin, statin plus 0.15% CoQ10 or 10% Ardisia japonica (AJB) leaves for 4 weeks. Plasma total cholesterol was significantly decreased in all groups fed statin containing diets compared with the control diet (p<0.01). Plasma and liver triglycerides were significantly decreased in group with statin plus CoQ10 compared with the control (both p<0.05). Maximum platelet aggregation was significantly higher in group with statin plus CoQ10 than other groups (p<0.05). Na‐K ATPase was increased in group with statin and decreased in group with statin plus CoQ10 and the difference between these two was significant (p<0.01). Na‐K cotransport and Na passive transport were significantly decreased in the control group compared with other groups (both p<0.05). Intracellular Na was the highest in group of statin and the lowest in group of statin plus CoQ10, correlating with Na‐K ATPase. TBARS productions in platelet rich plasma and liver tended to decrease in the groups with statin plus CoQ10 compared to other groups. sGOT and sGPT were significantly increased in group with statin compared with the control (p<0.05), and statin plus CoQ10 decreased the enzymes to the control levels.In present study, antioxidant rich AJB did not have positive effects in CVD parameters. Besides the beneficial effects as antioxidant and liver protection, statin plus CoQ10 seemed to decrease cholesterol more efficiently than statin alone.

Thermodynamic modeling to analyse composition of carbonaceous coatings of MnO and other oxides of manganese grown by MOCVD

Equilibrium thermodynamic analysis has been applied to the low-pressure MOCVD process using manganese acetylacetonate as the precursor. ``CVD phase stability diagrams'' have been constructed separately for the processes carried out in argon and oxygen ambient, depicting the compositions of the resulting films as functions of CVD parameters. For the process conduced in argon ambient, the analysis predicts the simultaneous deposition of MnO and elemental carbon in 1: 3 molar proportion, over a range of temperatures. The analysis predicts also that, if CVD is carried out in oxygen ambient, even a very low flow of oxygen leads to the complete absence of carbon in the film deposited oxygen, with greater oxygen flow resulting in the simultaneous deposition of two different manganese oxides under certain conditions. The results of thermodynamic modeling have been verified quantitatively for low-pressure CVD conducted in argon ambient. Indeed, the large excess of carbon in the deposit is found to constitute a MnO/C nanocomposite, the associated cauliflower-like morphology making it a promising candidate for electrode material in supercapacitors. CVD carried out in oxygen flow, under specific conditions, leads to the deposition of more than one manganese oxide, as expected from thermodynamic analysis ( and forming an oxide-oxide nanocomposite). These results together demonstrate that thermodynamic analysis of the MOCVD process can be employed to synthesize thin films in a predictive manner, thus avoiding the inefficient trial-and-error method usually associated with MOCVD process development. The prospect of developing thin films of novel compositions and characteristics in a predictive manner, through the appropriate choice of CVD precursors and process conditions, emerges from the present work.

Chemical vapor deposition of silicon nanodots on TiO2 submicronic powders in vibrated fluidized bed

Silicon nanodots have been deposited on TiO2 submicronic powders in a vibrated fluidized bed chemical vapor deposition (FBCVD) reactor from silane SiH4. Deposition conditions involving very low deposition rates have been studied. After treatment, powders are under the form of micronic agglomerates. In the operating range tested, this agglomerates formation mainly depends on the fluidization conditions and not on the CVD parameters. The best results have been obtained for anatase TiO2 powders for which the conditions of fluidization have been the most optimized. For these anatase powders, agglomerates are porous. SEM and TEM imaging prove that silicon nanodots (8–10 nm in size) have been deposited on the surface of particles and that this deposition is uniform on the whole powders and conformal around each grain, even if not fully continuous. Raman spectroscopy shows that the TiO2 powders have been partially reduced into TiO2−x during deposition. The TiO2 stoichiometry can be recovered by annealing under air, and IR spectroscopy indicates that the deposited silicon nanodots have been at least partly oxidized into SiO2 after this annealing.

Growth and characterization of diamond micro and nano crystals obtained using different methane concentration in argon-rich gas mixture

Diamond with different grain sizes and nanographite films were grown on silicon and diamond substrate using 90 vol.% argon in hydrogen and methane gas mixtures by hot filament chemical vapor deposition method (HFCVD). In current study, the methane volume concentration was varied from 0.125 to 2 vol. % in order to estimate its effect on film morphology. The substrate temperature was varied from 550 to 850 °C by external heating independently of other CVD parameters, in order to estimate the activation energy. Characterization techniques have involved Raman spectroscopy, high resolution X-ray difractometry and scanning electron microscopy. The CHEMKIN computer package has also been used to simulate the experiments. The results obtained here indicate a single mechanism for diamond growth but with a high competition with sp 2 phase's growth.

The Activation Energy for Nanocrystalline Diamond Films Deposited from an Ar/H<SUB>2</SUB>/CH<SUB>4</SUB> Hot-Filament Reactor

In this work we have investigated the effect of substrate temperature on the growth rate and properties of nanocrystalline diamond thin films deposited by hot filament chemical vapor deposition (HFCVD). Mixtures of 0.5 vol% CH4 and 25 vol% H2 balanced with Ar at a pressure of 50 Torr and typical deposition time of 12 h. We present the measurement of the activation energy by accurately controlling the substrate temperature independently of other CVD parameters. Growth rates have been measured in the temperature range from 550 to 800 degrees C. Characterization techniques have involved Raman spectroscopy, high resolution X-ray difractometry and scanning electron microscopy. We also present a comparison with most activation energy for micro and nanocrystalline diamond determinations in the literature and propose that there is a common trend in most observations. The result obtained can be an evidence that the growth mechanism of NCD in HFCVD reactors is very similar to MCD growth.

Thermodynamic analysis of growth of iron oxide films by MOCVD using tris(t-butyl-3-oxo-butanoato)iron(III) as precursor

Thermodynamic calculations, using the criterion of minimization of total Gibbs free energy of the system, have been carried out for the metalorganic chemical vapour deposition (MOCVD) process involving the β-ketoesterate complex of iron [tris(t-butyl-3-oxo-butanoato)iron(III) or Fe(tbob)3] and molecular oxygen. The calculations predict, under different CVD conditions such as temperature and pressure, the deposition of carbon-free pure Fe3O4, mixtures of different proportions of Fe3O4 and Fe2O3, and pure Fe2O3. The regimes of these thermodynamic CVD parameters required for the deposition of these pure and mixed phases have been depicted in a ‘CVD phase stability diagram’. In attempts at verification of the thermodynamic calculations, it has been found by XRD and SEM analysis that, under different conditions, MOCVD results in the deposition of films comprising pure and mixed phases of iron oxide, with no carbonaceous impurities. This is consistent with the calculations.

Diamond single crystal growth in hot filament CVD

The synthesis of diamond crystals is of particular interest due to the material's outstanding physical and mechanical properties. In hot filament CVD (HFCVD) we found a new process parameter window where the growth of single diamond volume crystals can be stabilized without the use of monocrystalline substrates. These CVD parameters are far beyond growth conditions for HFCVD diamond coating processes. Extremely low methane contents in the feed gas along with high substrate temperatures allow single diamond nuclei of a sufficiently large size to grow stabile. Crystals up to 80 μm in diameter were successfully synthesized. The morphology of the crystals is cubo-octaedric. According to our proposed growth model [S. Schwarz, C. Rottmair, J. Hirmke, S. Rosiwal, R.F. Singer, J. Cryst. Growth 271 (2004) 425.], the observed growth defects are primarily caused by the gas phase conditions during the CVD process. The aim of this work was to exclude a further possible formation of growth defects due to the employed diamond seed particles. The early growth stage was investigated by tracking distinct monocrystalline diamond seeds. It is shown that cubo-octaedric crystals with CVD typical smooth faces of high quality can be grown from micrometer-sized particles. Seed imperfections are therefore not considered as a major reason for growth defects of the larger crystals.

Effect of processing parameters on the nucleation behavior of nano-crystalline diamond film

The nucleation behavior of nanodiamond films and the associated electron field emission properties were investigated. Among the important CVD parameters, the methane/hydrogen ratio and the total pressure impose most markedly effect, whereas the microwave power and the boron content show least significant effect on the nucleation behavior for the nanodiamonds. Presumably, the prime factor modifying the rate of formation of diamond nuclei is the proportion of C +- and H +-species contained in the plasma. The bias voltage applied for nucleation of diamonds show more marked effect on improving the electron field emission capacity for the nanodiamonds than the boron-content does. It is ascribed to the increase in proportion of grain boundaries, as the grain boundaries are highly conductive and are good emission sites.

Deep Levels in As-Grown 4H-SiC Epitaxial Layers and their Correlation with CVD Parameters

Deep Levels in As-Grown 4H-SiC Epitaxial Layers and their Correlation with CVD Parameters